More than half the world's population carries the herpes simplex virus commonly known as oral herpes, a new report from the World Health Organization found.

The study, published Wednesday in the journal PLOS ONE, reports that 3.7 billion people under age 50 carry the type 1 (HSV-1) virus, which is is primarily transmitted through mouth-to-mouth contact and usually manifests as cold sores. That amounts to two-thirds of the world's population in that age group.

Herpes simplex virus type 2 (HSV-2) is nearly always transmitted through skin-to-skin contact and commonly causes genital herpes. WHO notes that the new estimates show that HSV-1 also is a notable cause of genital herpes when transmitted through oral sex.

Estimates for HSV-1 prevalence by region among people aged 0-49 in 2012